Wireless communication systems keep evolving to meet the needs for providing continuous and faster access to data networks. This evolution is driven by the desire for mobile users to be connected from anywhere at anytime to other users or information networks, for business, leisure or other purposes. In order to meet these needs, wireless communication systems may use multiple carriers for the transmission of data. A wireless communication system that uses multiple carriers for the transmission of data may be referred to as a multi-carrier system. The use of multiple carriers is expanding in both cellular and non-cellular wireless systems. A multi-carrier system may increase the bandwidth available in a wireless communication system according to a multiple of how many carriers are made available. For instance, dual carrier systems may double the bandwidth as a single carrier system and tri-carrier systems may triple the bandwidth as a single carrier system, etc. In addition to this throughput gain, diversity and joint scheduling gains may also be expected. This may result in improving the quality of service (QoS) for end users. Further, the use of multiple carriers may be used in combination with multiple-output (MIMO).
By way of example, in the context of Third Generation Partnership Project (3GPP) systems, a new feature called dual cell high speed downlink packet access (DC-HSDPA) has been introduced in Release 8 of the 3GPP specifications. In DC-HSDPA, the same geographical area is covered by up to two HSDPA, possibly adjacent, carriers in the same band. The use of frequency diversity between carriers in the same band in a DC-HSDPA system improves system performance. With DC-HSDPA, a base station (which may also be referred to as a Node-B, an access point, site controller, etc. in other variations or types of communications networks) communicates to a wireless transmit/receive unit (WTRU) over two downlink carriers simultaneously. This not only doubles the bandwidth and the peak data rate available to WTRUs, but also has a potential to increase the network efficiency by means of fast scheduling and fast channel feedback over two carriers.